Conventional stud welders use solenoids to control the back and forth movement of the welding gun from a retracted position to an operative position in which the stud is juxtaposed to a metal part to which it is to be welded. Such welders must be adjusted for each different type of weld. Since the stroke of a solenoid is inherently short, because the position of the workpiece to which welding must be accomplished varies over a range larger than the stroke of the solenoid, and because the amount which the stud "sticks out" from the welding head varies, a clutch must be used to compensate for this variation. Clutches, however, introduce additional complexity, expense and reliability problems.
The reliability of welders could be improved and their expense reduced by using an actuator with a long stroke. Typically, a suitably long stroke would be about 10 mm. Such a stroke would allow the elimination of a clutch.
U.S. Pat. No. 5,252,802 issued to Raycher and its continuation which issued as U.S. Pat. No. 5,321,226, also to Raycher, both disclose a stud welder with a linear actuator that employs position control. The actuator utilizes a movable permanent magnet around which is wound a fixed coil formed of two sets of opposed windings. The large mass of the permanent magnet limits its acceleration and deceleration and, therefore, limits its response. Although the total weld time is long compared to the time for the actuator to move from one position to the next, the latter time is still significant and shortening it can improve productivity.
Accordingly, it is an object of the invention to provide an improved stud welder. It is a further object of the invention to provide a stud welder that is capable of faster operation than hitherto known welders.